For unmanned aircraft (UA) to operate effectively, they need the ability to see and avoid other aircraft in the same way that manned aircraft do. One of the challenges to avoiding other aircraft without an on-board pilot is having the ability to see them electronically. Aircraft equipped with a cooperative surveillance source such as an operational transponder device are referred to as cooperative targets and can be seen electronically by interrogating the cooperative surveillance source. Aircraft that are not equipped with a cooperative surveillance source are referred to as non-cooperative targets. Non-cooperative targets must be seen with a non-cooperative surveillance method.
Radar is one non-cooperative surveillance method. Challenges with using radar to track aircraft include significant and expensive processing requirements, which scale with the number of targets that must be tracked. Radar systems typically track both non-cooperative and cooperative targets, which increases the processing requirements as compared to tracking solely non-cooperative targets.